basically ... they are middleman ... you dont need to read up on paperworlds for export and import especially you bring in bulk items (not bulk until can set up a factory lar, but like 50 - 100 kilos of fashion jeans ((yes, they go by kilos not by piece))

in terms of payment .... You -- Forwarder -- Seller (you dont need to go through those nasty bank transfer etc .... and, not all merchants accept CC in china, again, regulation)
in terms of product ...... Seller -- Forwarder -- You (import/export paperwork)

some sellers in china find it easier to deal with forwarders as they understand the procedure there .... some more, their banks are highly regulated by the gov and currency ?? RMB/Yuan only got accepted into the currency basket (like a few days ago??)

i deal with them when bring in heavy bulky items, or items that kastam will likely kacau (electronic items?) ... like industrial ventilation fans etc (i mod it into a filter) .... i will go by their recommendation like how to avoid, if not minimize duit derma